Sapling Biology Assignment 9

Which of the following is the simplified chemical equation for cellular respiration?

C6H12O6 + 6O2 → 6H2O + 6CO2

Which steps of cellular respiration generate NADH or FADH2 as products, and which steps receive those molecules as inputs?

Generates NADH or FADH2: Glycolysis Acetyl CoA Production Citric acid cycle Receives NADH or FADH2: Oxidative phosphorylation

Carbon dioxide is one of the products of the citric acid cycle, or Krebs cycle. Click on an arrow in the diagram below that coincides with a step at which CO2 is produced.

alpha - ketoglutarate

Place the stages of cellular respiration in the order they occur.

1. Glycolysis 2. Conversion of pyruvate to acetyl-CoA 3. Citric acid cycle 4. Electron transport chain

Arrange the steps of ATP generation by ATP synthase in the order that they occur.

1. Hydrogen ion gradient is established between the inter membrane space and the mitochondrial matrix. 2. Hydrogen ions move down their gradient through a channel in ATP synthase. 3. Hydrogen ions cause the F0 portion of ATP synthase to spin. 4. Catalytic sites in the F1 portion of ATP synthase phosphorylate ADP.

The pyruvic acid from glycolysis can be converted to acetic acid, which can enter the citric acid cycle. Because this process is a cycle, the atoms entering the cycle must balance the atoms that leave. Consider carbon balance in the citric acid cycle. How many CO2 molecules leave the cycle for each acetic acid molecule that enters? For this question, assume that carbon only enters as acetic acid and exits as CO2. Note that acetic acid has two carbon atoms. You can determine the number of carbon atoms in carbon dioxide from its formula, CO2.

2 CO2 for every acetic acid molecule Using the above answer, how many molecules of CO2 are directly generated by the citric acid cycle from 3 molecules of acetic acid? Again, in this question assume that carbon only enters as acetic acid and exits as CO2. 6 CO2 per 3 acetic acid

2,4-dinitrophenol (DNP) was a popular ingredient in diet pills in the 1930s before it was discovered that the moderate doses of the compound cause exceptionally high body temperature and even death. Complete the following passages detailing how DNP's mechanism of action explains why it causes both high body temperature and weight loss.

2,4-dinitrophenol (DNP) causes PROTONS to pass directly across the inner mitochondrial membrane instead of returning to the mitochondrial matrix through ATP SYNTHASE proteins. Because of DNP's effect on the mitochondrion, less energy is captured in the form of ATP and more energy is instead wasted as heat.

During glycolysis, glucose is broken down into two molecules of pyruvic acid. How many carbon atoms are in each pyruvic acid molecule?

3 carbon atoms

Glycolysis is a series of chemical reactions that convert glucose to pyruvic acid. Glycolysis also uses and generates chemical energy. Several compounds are necessary for glycolysis. These compounds are also components of other metabolic pathways in the cell. Match the compounds in the drop-down menus on the right with the descriptions on the left. You will not select all the compounds. You may select any compound more than once.

A carbohydrate that enters glycolysis directly: Glucose The direct energy source for glycolysis: ATP An end product that is modified to enter the citric acid cycle: Pyruvic acid A product that donates electrons to the electron transport chain: NADH A product that can be used directly for energy: ATP

Cellular respiration is carried out in the presence of oxygen (aerobic conditions) or the absence of oxygen (anaerobic conditions). Determine whether each of the following occur under aerobic conditions, anaerobic conditions, or both aerobic and anaerobic conditions.

Aerobic conditions: Citric acid cycle (Krebs cycle) Electron transport chain Anaerobic conditions: Fermentation Both: Glycolysis

Osmosis is the movement of water across a semi-permeable membrane from a region of low to high solute concentration. Considering the definition of osmosis, which of the following statements describe chemiosmosis?

Movement of ions across a semipermeable membrane from a region of high to low ion concentration.

The reaction pictured below is an oxidation-reduction in the citric acid cycle in which the energy-carrier molecule, NADH, is generated. Identify which molecule in the reaction is oxidized and which molecule is reduced.

Oxidized: malate Reduced: NAD+

Cellular respiration consumes glucose during glycolysis. What product of glycolysis can be subsequently modified to enter the citric acid cycle under aerobic conditions?

Pyruvate

Pyruvate is a product of glycolysis and is subsequently converted to acetyl-CoA. Acetyl-CoA ia a substrate for the citric acid cycle (CAC). Exactly how many molecules of glucose must be oxidized in glycolysis to provide the input for 12 turns of the CAC?

6

The electron transport chain consists of protein complexes embedded in the inner mitochondrial membrane, where is generates a proton gradient by a series of oxidation-reduction, or redox, reactions. Although all the stages of cellular respiration (glycolysis, the citric acid cycle, and the electron transport chain) are necessary for life, the electron transport chain is sometimes called the most important stage.

Complete the sentence: The electron transport chain uses the transfer of ELECTRONS between protein complexes to set up a proton gradient. What is the function of the proton gradient in the mitochondrion? It is potential energy that the cell uses to generate ATP.

In general, what happens during an oxidation-reduction reaction between two molecules?

An atom in the oxidized molecule donates an electron as an atom in the reduced molecule attracts the electron.

Identify compounds that are required for the electron transport chain and compounds that are produced by the electron transport chain. Not all the potential reactants or products are given. Place all the compounds.

Compounds that enter the electron transport chain: NADH, FADH2, O2, ADP Compounds produced by the electron transport chain: NAD+, FAD, H2O, ATP

Below are events that occur during cellular respiration. Identify where each of the events occur within a eukaryotic cell. Each cellular location may be used once, more than once, or not at all.

Conversion of pyruvate to acetyl-CoA: Mitochondrial matrix Electron transport chain: Mitochondrial membrane Breakdown of glucose to pyruvate: Cytosol Citric acid cycle: Mitochondrial matrix

Anaerobic respiration allows a cell to break down carbohydrates in the absence of oxygen. Identify how NAD + is used by animal cells during anaerobic respiration.

During fermentation, NAD+ is generated from NADH and is used to continue glycolysis.

In eukaryotic cells, each stage of cellular metabolism generates a different net amount of ATP. Which stage directly generates the greatest number of ATP molecules per metabolized glucose molecule?

Electron transport chain and ATP synthase

Compare and contrast lactic acid fermentation and ethanol fermentation (alcohol fermentation). Move each phrase the the appropriate category. If a phrase describes both types of fermentation, classify it as both.

Ethanol fermentation: -Used by yeast cells - Generates ethanol Both: - Regenerates NAD+ that can be used in glycolysis - Occurs under anaerobic conditions Lactic acid fermentation: - Used by animal cells - Produces lactic acid (lactate)

When a person is sprinting, the person's muscle cells will begin using anaerobic respiration in addition to keeping the mitochondria respiring aerobically as much as the oxygen supply will allow. What benefits do muscle cells gain from anaerobic respiration in this situation?

For every glucose molecule that enters glycolysis, the cell generates, without oxygen, two ATP molecules that can keep the muscles moving. Adding electrons from NADH to pyruvate regenerates NAD+, so that glycolysis can continue, and produces lactic acid, a waste product that can diffuse out of the cell.

A proton gradient is formed in the mitochondria such that the concentration of protons (H+) is higher on one side of the inner mitochondrial membrane that on the other side. What is the purpose of this proton gradient?

Generates ATP in the electron transport chain.

Electron carrier molecules transfer electrons between metabolic pathways. Choose the electron carriers that transfer electrons from glycolysis to the electron transport chain and from the citric acid cycle to the electron transport chain. One of the molecules will be placed more than once, and one answer box will have two molecules.

Top answer box: NADH Bottom answer box: NADH and FADH2

Although the path of one glucose molecule through glycolysis generates a total of four ATP molecules, there is a net gain of only two ATP for each glucose molecule that enters the pathway. Why does the passage of one glucose molecule through glycolysis have a payoff of only two ATP molecules?

Two ATP molecules are used in the initial phase of glycolysis, reducing the net gain to two ATP.